The present invention relates to a rotor for a salient-pole machine and, more particularly, to an improvement in ventilation grooves provided on an outer periphery of a rotor rim for cooling magnetic poles.
FIGS. 5 and 6 show a portion of a conventionally employed structure of a rotor of the above-mentioned type. As shown in FIG. 5, a rotary shaft 1 has a spider 2 mounted thereto, with a rotor rim fixed on the outer periphery thereof. The rotor rim 3 is formed on its outer periphery with a plurality of dovetail grooves 5, each of which has a magnetic pole 4 rigidly secured therein. Previously, the rotor of this type only a narrow space between respective adjacent poles, is typically provided on an outer peripheral portion of the rotor rim, between respective adjacent poles, with an U shaped ventilation groove 7, such as disclosed, for example, in Japanese Utility Model Examined Publication No. 40-5927, for the purpose of maintaining a ventilation space to provide for an improved cooling effect.
More specifically, in FIGS. 5 and 6, if it is desired to have cooling air effectively come into contact with coils 6 of the magnetic poles 4 in order to adequately cool the coils 6, the cooling air has to be spread over the whole length of each pole 4 in the axial direction before flowing into the coils 6. For this purpose, the rotor rim 3 has been provided on its outer periphery with the U shaped ventilation grooves 7 through which the cooling air, as shown by arrows E and F, can be distributed over the whole axial length of each magnetic pole 4 and then caused to radially flow toward and effectively cool the coils 6.
Further, since each pole 4, when rotated, undergoes centrifugal force, shown by arrows P, a dovetail joint has been adopted for connecting the pole 4 to the rotor rim 3, that is, the pole 4 is arranged to be capable of staying at its prescribed location against centrifugal force P by the dovetail joint portion. Components Q of centrifugal force P act on the dovetail joint.
In such a prior art construction, between the dovetail groove 5 and the U shaped ventilation groove 7, the portion between points A and B or C and D necessarily becomes susceptible to breakage when considered from the standpoint of strength. Due to the component Q of centrifugal force P acting upon the pole 4, shearing stress results in the portion A-B or C-D due to the component Q and the bending stress due to a bending moment Q.times.l and the portion is required to endure such resultant stress, but some of the existing machines have shortcomings that if said portion is designed to have a dimension required from a viewpoint of strength, it becomes impossible to provide an effective ventilation groove.